Although microfluid components were developed years ago for analytical applications, microengineering techniques have only recently been applied to the development of equipment for chemical synthesis, so-called microreactors. Principle components of such microreactors are mixers and heat exchangers. Conventional static micromixers work according to the principle of multilamination to ensure rapid mixing by diffusion. This is the only mixing mechanism that can be used with laminar flows in microchannels. The creation of alternating laminations by means of geometric parameters allows good mixing in the microscopic range.
The publication Int. Eng. Chem. Res. 1999, 38, 1075–1082, W. Ehrfeld et al., describes a generic micromixer. This single mixer comprises three components: a galvanically and X-ray lithographically structured plate having a mixing zone and two feeding chambers and a two-piece casing in which the plate is set. A means for the supply of reactant and the discharge of the product are provided in the upper section of the casing.
The single mixer has two mixer cells with a common mixing zone. The two fluid reactants are fed into the mixing chambers and split into partial flows in the digital channels. The partial flows of one reactant are not in contact with the partial flows of the other reactant—they are separated from one another by microwalls in the form of ribs. The two reactants first come in contact with one another in the port zone, which is above and perpendicular to the digital channels. The product is discharged from the casing through the ports. The pressure drop in the mixing zone is set by means of the port width.
A significant disadvantage of this single mixer is that its throughput is very limited. With a pressure drop of approx. 1.2 bar, throughput is only 0.8 l/h. Because of this low throughput, use of the single mixer for large-scale chemical production is limited. In an attempt to alleviate this problem, 10 single mixers were arranged in parallel in one casing, with the reactants supplied to the individual micromixers from a common source. The single mixers were arranged in a star configuration, with the supply line for one reactant in the center of the star and the supply lines for the other reactant running around the outside of the star (at the indicated locations). But this measure only resulted in increasing throughput from 0.8 l/h to approx. 3 l/h with a pressure drop of approx. 1.2 bar.